Induction and suppression of cross-reactive antituberculosis immunity after Mycobacterium lepraemurium infection of mice.

Mice immunized with 10(8) live Mycobacterium lepraemurium in the footpad showed increased resistance to infection with BCG or M. tuberculosis R1Rv. This resistance could be transferred adoptively with lymphoid cells, signifying that the immunity was cross-reactive rather than nonspecific. Adoptive cross-reactive immunity to M. tuberculosis was also conferred by spleen cells from mice immunized with large doses of living or dead M. lepraemurium intravenously, a route of immunization that suppresses the induction of cell-mediated immunity to that organism. The presence of specific suppressor activity was sought in mice immunized intravenously with M. lepraemurium. It was found that mice preimmunized intravenously with living or dead M. lepraemurium and then infected with BCG did not confer levels of adoptive antituberculosis immunity as high as those conferred by mice immunized with BCG alone. Similarly, a mixture of BCG-sensitized and M. lepraemurium-sensitized cells did not convey as much immunity as BCG-sensitized cells alone, signifying suppression of the effector lymphocytes.     

Mycobacterium bovis BCG induces similar immune responses and protection by rectal and parenteral immunization routes

We compared cellular immune responses to rectal, subcutaneous, and intradermal administration of Mycobacterium bovis BCG for 5 to 20 weeks in mice, guinea pigs, and macaques. Strong lymphoproliferative responses were induced in spleen cells after in vitro stimulation with purified protein derivative in guinea pigs and macaques, whatever the route of immunization. Comparable high numbers of gamma interferon- and tumor necrosis factor alpha-producing cells were found in the spleen after rectal, subcutaneous, and intradermal immunization of mice and macaques. Similar levels of precursors of cytotoxic T lymphocytes specific for mycobacterial antigens were observed in mice for all immunization routes. In macaques, cytotoxic activity, determined only at the end of the experiment (20 weeks), was similar after rectal and intradermal immunization. Six months after immunization, rectal and subcutaneous routes induced in mice similar levels of protective immunity against challenge with a virulent Mycobacterium tuberculosis strain (H37Rv). Rectal immunization gave immune responses and protective capacity similar to those for parenteral immunization and seemed to be a promising new route of vaccination against tuberculosis; in our study, immunization via the rectal route never induced side effects associated with parenteral routes (axillary adenitis) and could also effectively reduce the risks of viral transmission associated with unsafe injections in the developing world.     

Vaccination with a Sindbis virus-based DNA vaccine expressing antigen 85B induces protective immunity against Mycobacterium tuberculosis

To improve DNA vaccination against Mycobacterium tuberculosis, we evaluated the effectiveness of a Sindbis virus-based DNA construct expressing the tuberculosis antigen 85B (Sin85B). The protective efficacy of Sin85B was initially assessed by aerogenically challenging immunized C57BL/6 mice with virulent Mycobacterium tuberculosis. At 1 and 7 months postinfection, the lung bacterial burdens were considerably reduced and the lung pathology was improved in vaccinated mice compared to naive controls. Furthermore, the mean survival period for Sin85B-immunized mice (305 +/- 9 days) after the tuberculous challenge was extended 102 days relative to the naive mice (203 +/- 13 days) and was essentially equivalent to the survival time of Mycobacterium bovis BCG-vaccinated mice (294 +/- 15 days). The essential role of gamma interferon (IFN-gamma) in Sin85B-mediated protection was established by showing that significantly increased levels of IFN-gamma mRNA were present postinfection in lung cells from vaccinated mice relative to control mice and by demonstrating that IFN-gamma depletion prior to challenge abolished the vaccine-induced protection. The substantial antituberculosis protective responses induced by Sin85B immunization of CD4-/- mice strongly suggested that CD8 cells partially mediate Sin85B-induced protective immunity. Interestingly, Sin85B vaccination did not protect RNase L-/- (a key enzyme in the innate antiviral response) mice while significant protection was detected in RNase L-/- mice immunized with either BCG or a conventional DNA plasmid expressing antigen 85B. These data show that immunization with Sin85B offers protection similar to BCG in a murine model of pulmonary tuberculosis and suggest that Sin85B-induced protection is dependent upon both innate and acquired immune mechanisms.     

Induction of Cell-Mediated Immunity against Mycobacterium tuberculosis Using DNA Vaccines Encoding Cytotoxic and Helper T-Cell Epitopes of the 38-Kilodalton Protein

Cell-mediated immune responses are crucial in the protection against tuberculosis. In this study, we constructed DNA vaccines encoding cytotoxic T lymphocytes (CTL) and T helper cell (Th) epitopes of the 38-kDa lipoglycoprotein of Mycobacterium tuberculosis and analyzed and compared their immunogenicities with that of pXJ38, a DNA vaccine encoding the entire 38-kDa protein (X. Zhu, N. Venkataprasad, H. S. Thangaraj, M. Hill, M. Singh, J. Ivanyi, and H. M. Vordermeier, J. Immunol. 158:5921-5926, 1997). Plasmid DNAs encoding a CTL epitope, P3 (pP3), a Th epitope (vTh), or both the Th and the P3 epitopes (pThP3) were prepared and tested in C57BL6/J (H-2(b)) mice. Our results confirmed that DNA immunization with pXJ38 induces strong CD8(+) CTL and Th1 responses (high gamma interferon [IFN-gamma], low interleukin-4 [IL-4]). Coadministration of plasmid DNAs encoding a Th epitope with those encoding a CTL epitope (vTh+pP3) elicited both antigen-specific CD8(+) CTL and Th1 responses. High levels of IFN-gamma were secreted by spleen cells from all plasmid DNA-vaccinated mice after in vitro stimulation with the recombinant 38-kDa protein. Small or undetectable amounts of IL-4 were observed, which indicates the induction of a Th1-like response. Multiple-epitope vaccination by vTh+pP3 or pThP3 resulted in a broader Th1 response to peptide or epitopes than the single-epitope plasmid DNAs. Antigen-specific immunoglobulin G2a was only detected in sera from mice immunized with the plasmid pXJ38, and not in mice immunized with the epitope-based DNA vaccines. Thus, the absence of an antibody response after immunization with epitope plasmid DNAs and their ability to trigger only a specific cellular immune response may prove to be important advantages for a vaccine against tuberculosis.     

Influenza virus NS vectors expressing the mycobacterium tuberculosis ESAT-6 protein induce CD4+ Th1 immune response and protect animals against tuberculosis challenge

Infection with Mycobacterium tuberculosis remains a major cause of morbidity and mortality all over the world. Since the effectiveness of the only available tuberculosis vaccine, Mycobacterium bovis bacillus Calmette-Guérin (BCG), is suboptimal, there is a strong demand to develop new tuberculosis vaccines. As tuberculosis is an airborne disease, the intranasal route of vaccination might be preferable. Live influenza virus vaccines might be considered as potential vectors for mucosal immunization against various viral or bacterial pathogens, including M. tuberculosis. We generated several subtypes of attenuated recombinant influenza A viruses expressing the 6-kDa early secretory antigenic target protein (ESAT-6) of M. tuberculosis from the NS1 reading frame. We were able to demonstrate the potency of influenza virus NS vectors to induce an M. tuberculosis-specific Th1 immune response in mice. Moreover, intranasal immunization of mice and guinea pigs with such vectors induced protection against mycobacterial challenge, similar to that induced by BCG vaccination.     

Flagellin as a good carrier and potent adjuvant for Th1 response: study of mice immune response to the p27 (Rv2108) Mycobacterium tuberculosis antigen

We have recently expressed and characterized the product of the gene Rv2108 of Mycobacterium tuberculosis (MT), the p27 protein. Here, we investigated the immune responses against the p27 protein in the context of different pathogen associated molecular patterns (PAMPs). Different immunization protocols were used. BALB/c mice were immunized either with the p27 recombinant protein in Freund's adjuvant or in phosphate saline buffer (PBS), with a pcDNA3 plasmid containing the gene encoding the p27 protein, or with the Escherichia coli bacteria expressing the p27 protein genetically fused into the flagellin. We found that p27 expressed into the flagellin led to the strongest cellular responses, where we obtained the highest production of IFN-gamma and cell proliferation, an indication of specific Th1-like orientation of the immune response. We confirmed the role of flagellin in this response by using different immunization combinations.     

Th1 adjuvant N-acetyl-D-glucosamine polymer up-regulates Th1 immunity but down-regulates Th2 immunity against a mycobacterial protein (MPB-59) in interleukin-10-knockout and wild-type mice.

Treatment of mice with heat-killed (HK) Mycobacterium bovis BCG or 1- to 10-microm chitin particles (nonantigenic N-acetyl-D-glucosamine polymers) is known to induce innate immune responses, including gamma interferon (IFN-gamma) production, which plays a Th1 adjuvant role. However, HK BCG further induces prostaglandin E2-releasing spleen macrophages (Mphi) (PGE2-Mphi), which potentially inhibit Th1 adjuvant activities. We found that chitin particles did not induce PGE2-Mphi formation. To further assess whether chitin has Th1 adjuvant effects, interleukin-10 (IL-10)-knockout (KO) mice and their wild-type (WT, C57BL/6) controls were immunized with a 30-kDa MPB-59 mycobacterial protein mixed with chitin. Immunization with MPB-59 alone induced Th2 responses, characterized by increases in total serum immunoglobulin E (IgE) and specific serum IgG1 levels and spleen Th2 cells producing IL-4, IL-5, and IL-10. No IFN-gamma-producing spleen Th1 cells, specific serum IgG2a, or delayed-type hypersensitivity (DTH) footpad reactions were detected. On the other hand, chitin-MPB-59 immunization significantly increased spleen Th1 responses, DTH reaction, and serum IgG2a levels along with decreases of Th2 responses. The magnitude of these Th1 adjuvant effects was greater in IL-10-KO mice than in WT mice. In contrast, immunization with HK BCG-MPB-59 showed little or no Th1 adjuvant effect. These data indicate that chitin has a unique Th1 adjuvant effect on the development of Th1 immunity against a mycobacterial antigen. IL-10 down-regulates the adjuvant effect of chitin.     

DNA vaccine encoding ESAT-6 enhances the protective efficacy of BCG against Mycobacterium tuberculosis infection in mice

ESAT-6 is a protein produced by virulent Mycobacterium tuberculosis but absent in Mycobacterium bovis bacillus Calmette-Guerin (BCG) and is considered as a promising vaccine subunit against tuberculosis. The protective efficacy of a new strategy based on the combination of DNA vaccine encoding ESAT-6 (DNA-E6) and BCG immunization was investigated in the present study. BALB/c mice were immunized with DNA-E6, BCG, DNA-E6 plus BCG, vector plus BCG or vector alone. Three weeks after the last immunization, antigen-specific interferon (IFN)-gamma secreted upon stimulation with BCG-PPD or ESAT-6 protein by splenocytes of the different groups was determined by an ELISA. The immunized mice were challenged intravenously with low-dose virulent M. tuberculosis H37Rv and bacterial load of the infected mice was measured in the spleen and lung 6 weeks later. Pathological changes in the lung were observed by haematoxylin-eosin (HE) or acid-fast staining. Our study demonstrated that ESAT-6-specific IFN-gamma was improved in mice vaccinated with DNA-E6 plus BCG, compared with those mice immunized with BCG alone. The combination of DNA-E6 and BCG resulted in the maximum reduction in bacterial load in both the lung and spleen, and only slight pathological changes were detected in the lung. These results suggested that the combination of DNA-E6 and BCG vaccination could be a better strategy against M. tuberculosis infections in human.     

Priming by DNA immunization augments protective efficacy of Mycobacterium bovis Bacille Calmette-Guerin against tuberculosis

Sequential immunization with mycobacterial antigen Ag85B-expressing DNA and Mycobacterium bovis bacille Calmette-Guerin (BCG) was more effective than BCG immunization in protecting against Mycobacterium tuberculosis infection. Depletion of the CD8(+) T cells in the immunized mice impaired protection in their spleens, indicating that this improved efficacy was partially mediated by CD8(+) T cells.     

pBudCE4.1/PPE68DNA疫苗诱导Balb/c小鼠产生Th1免疫应答

目的构建结核分枝杆菌PPE68 DNA疫苗,并探讨其在小鼠体内诱导的Th1免疫应答。方法将结核分枝杆菌PPE68基因和复制子OriM基因亚克隆入真核表达质粒pBudCE4.1中构建穿梭质粒,并用其免疫Balb/c小鼠,于第3次免疫后2周处死小鼠,分别检测免疫小鼠血清IgG2a水平、IFN-γ和IL-12水平;特异性蛋白刺激后淋巴细胞增殖状态;小鼠肺、脾组织病理改变情况。结果 PPE68 DNA疫苗免疫小鼠后血清中的IgG2a水平、IFN-γ和IL-12均有意义的提高,脾淋巴细胞增殖显著。脾肺未见明显病理改变。结论 PPE68DNA疫苗可有效诱导小鼠Th1免疫应答,为进一步研究其抗MTB的免疫保护作用奠定了基础。     

Effects of DNA- and Mycobacterium bovis BCG-based delivery of the Flt3 ligand on protective immunity to Mycobacterium tuberculosis

The control of intracellular pathogens such as Mycobacterium tuberculosis is dependent on the activation and maintenance of pathogen-reactive T cells. Dendritic cells (DCs) are the major antigen-presenting cells initiating antimycobacterial T-cell responses in vivo. To investigate if immunization strategies that aim to optimize DC function can improve protective immunity against virulent mycobacterial infection, we exploited the ability of the hematopoietic growth factor Fms-like tyrosine kinase 3 ligand (Flt3L) to expand the number of DCs in vivo. A DNA fusion of the genes encoding murine Flt3L and M. tuberculosis antigen 85B stimulated enhanced gamma interferon (IFN-gamma) release by T cells and provided better protection against virulent M. tuberculosis than DNA encoding the single components. Vaccination of mice with a recombinant Mycobacterium bovis BCG strain secreting Flt3L (BCG:Flt3L) led to early expansion of DCs compared to immunization with BCG alone, and this effect was associated with increased stimulation of BCG-reactive IFN-gamma-secreting T cells. BCG and BCG:Flt3L provided similar protective efficacies against low-dose aerosol M. tuberculosis; however, immunization of immunodeficient mice revealed that BCG:Flt3L was markedly less virulent than conventional BCG. These results demonstrate the potential of in vivo targeting of DCs to improve antimycobacterial vaccine efficacy.     

Skewing of the Th1/Th2 responses in mice due to variation in the level of expression of an antigen in a recombinant BCG system

In spite of rapid developments in the study of mycobacteria during the last two decades, tuberculosis (TB) has maintained its status as the leading killer among all infectious diseases. Extensive evidence exists to support a central role for a T-helper type 1 (Th1) immune response for protection against TB in mice and humans. Bacille Calmette-Guerin (BCG), the only vaccine against TB, although not perfect in its ability to protect against the adult form of TB, is a strong inducer of Th1 responses and is being increasingly used as a delivery vehicle for the presentation of foreign antigens to the immune system. It has been proposed that expression of immunodominant antigens or cytokine genes in BCG can enhance the ability of BCG to induce a Th1 immune response. Since dose of the antigen is considered as one of the parameters that influence the Th cell responses, the level of expression of the candidate antigen should influence the final Th response against the recombinant BCG (rBCG). In the present study, the effect of over-expression of a candidate antigen Antigen 85B (Ag 85B) in a rBCG system, on the Th-priming ability of BCG has been investigated in the murine model. BALB/c mice were immunized with three different rBCG constructs expressing Ag 85B to various levels. Induction of Th1/Th2 responses was analyzed by measuring levels of interferon-gamma (Th1) and interleukin-10 (Th2) in antigen-stimulated splenocyte cultures and by quantifying the antigen-specific IgG2a (Th1) and IgG1 (Th2) antibody responses. By varying the level of expression of Ag 85B, specific immune responses against Ag 85B were observed to range from mixed Th1/Th2 to Th1. However, the BCG-specific immune responses in case of all rBCG-immunized animals remained predominantly Th1.     

IL-23-dependent IL-17 drives Th1-cell responses following Mycobacterium bovis BCG vaccination

The generation of effective type 1 T helper (Th1)-cell responses is required for immunity against intracellular bacteria. However, some intracellular bacteria require interleukin (IL)-17 to drive Th1-cell immunity and subsequent protective host immunity. Here, in a model of Mycobacterium bovis Bacille Calmette-Guerin (BCG) vaccination in mice, we demonstrate that the dependence on IL-17 to drive Th1-cell responses is a host mechanism to overcome bacteria-induced IL-10 inhibitory effects. We show that BCG-induced prostaglandin-E2 (PGE2) promotes the production of IL-10 which limits Th1-cell responses, while simultaneously inducing IL-23 and Th17-cell differentiation. The ability of IL-17 to downregulate IL-10 and induce IL-12 production allows the generation of subsequent Th1-cell responses. Accordingly, BCG-induced Th17-cell responses precede the generation of Th1-cell responses in vivo, whereas the absence of the IL-23 pathway decreases BCG vaccine-induced Th17 and Th1-cell immunity and subsequent vaccine-induced protection upon M. tuberculosis challenge. Importantly, in the absence of IL-10, BCG-induced Th1-cell responses occur in an IL-17-independent manner. These novel data demonstrate a role for the IL-23/IL-17 pathway in driving Th1-cell responses, specifically to overcome IL-10-mediated inhibition and, furthermore, show that in the absence of IL-10, the generation of BCG-induced Th1-cell immunity is IL-17 independent.     

Recombinant BCG coexpressing Ag85B,ESAT-6 and Rv3620c elicits specific Th1 immune responses in C57BL/6 mice

Tuberculosis (TB) remains to be an enormous global health problem. The inconsistent protection efficacy of Bacille Calmette-Guérin (BCG) calls for new vaccines for TB. One choice to improve the efficacy of BCG vaccine is recombinant BCG (rBCG). Experimental evidences have revealed that Ag85B, ESAT-6 and Rv3620c are important immunodominant antigens of Mycobacterium tuberculosis. In this study, we have constructed a novel rBCG expressing fusion protein Ag85B-ESAT6-Rv3620c and evaluated the immunogenicity of this rBCG in C57BL/6 mice. Results show that there is a strong TB-specific CD4⁺ and CD8⁺ T lymphocytes proliferation in mice immunized with this rBCG vaccine. A single dose immunization of rBCG could induce a significantly strong Th1 immune response characterized by an increasing ratio of antigen-specific IgG2b/IgG1 as well as a high expression level of Th1 cytokines such as IFN-γ, TNF-α and IL-2. This conclusion was confirmed by a decreased secretion of Th2 cytokine IL-10. Moreover, this rBCG induced a strong humoral response in mice with an increasing antigen-specific IgG titer. Therefore, we concluded that this rBCG could significantly increase both Th1 type cellular immune response and antigen-specific humoral response compared with BCG. The above observations demonstrated that rBCG::Ag85B-ESAT6-Rv3620c is a potential candidate vaccine against M. tuberculosis for further study.     

Analysis of recombinant mycobacteria as T helper type 1 vaccines in an allergy challenge model

The potential for development of mycobacteria as T helper type 1 (Th1) vaccines capable of induction of Th1 responses to recombinant antigens was explored in a model system based on an immunodominant peptide from house dust mite. Different recombinant mycobacterial preparations were compared for their ability to induce a Th1 response to the peptidea. It was found that mycobacterial viability was not a prerequisite for Th1 immunogenicity. A dominant interferon-gamma (IFN-gamma) response to peptide was observed in splenocytes from C57BL/6J mice immunized with live or heat-killed preparations of recombinant Mycobacterium vaccae or with live attenuated bacillus Calmette-Guèrin (BCG) vaccine expressing the antigen. Interleukin-5 (IL-5), a marker of a Th2 response, was detected only in mice receiving live M. vaccae. A similar pattern was observed in BALB/b mice, although the magnitude of the IFN-gamma response was much lower. Control and immunized mice were subsequently exposed to allergen using a Th2-inducing challenge protocol. A significant shift from a Th2 to a Th1 response was observed in immunized mice, as judged by cytokine expression by splenocytes and by subclass of circulating antibody. The effect was seen in three inbred mouse strains differing in their innate bias towards Th1 or Th2 responses. It was dependent on the presence of specific antigen in the mycobacterial preparation and, under the immunization conditions tested, was more pronounced with dead M. vaccae than with live BCG as carrier vaccine. The results demonstrate the potency of killed mycobacteria as Th1 adjuvants and suggest a potential application for recombinant mycobacteria in antigen-specific immune modulation.     

Modulation of pulmonary DC function by vaccine‐encoded GM‐CSF enhances protective immunity against Mycobacterium tuberculosis infection

The rational design of new vaccines engineered to target key components of the host immune response is crucial to aid control of important infectious diseases such as tuberculosis. In this report, we determined whether modifying the function of pulmonary APC could improve protection against infection with Mycobacterium tuberculosis. Targeted delivery to the lung of the cytokine GM‐CSF, expressed by the Mycobacterium bovis BCG vaccine strain, increased pulmonary DC numbers and secretion of the immunoregulatory cytokine IL‐12, compared with parental BCG immunization. This impact on APC number by BCG:GM‐CSF resulted in accelerated priming of antigen‐specific CD4⁺ T cells in the mediastinal lymph nodes and increased migration of activated CD4⁺ T cells into the lung. i.n. administration of BCG:GM‐CSF resulted in significantly increased protection against M. tuberculosis infection compared with mice vaccinated with BCG alone. BCG:GM‐CSF exhibited an improved safety profile, as immunodeficient RAG1^?/? mice vaccinated i.n. with BCG:GM‐CSF survived significantly longer than control BCG‐vaccinated mice. These data demonstrate that manipulating immune cells in the lung by BCG‐based delivery of GM‐CSF can assist the development of protective mucosal immunity against pulmonary bacterial infection.     

二甲基三十六烷基铵及卡介苗多糖核酸佐剂在结核亚单位疫苗加强BCG免疫中的效应研究

目的 探讨二甲基三十六烷基铵(dimo-thylidioctyl ammonium bromide,DDA)和卡介苗多糖核酸(BCC-PSN)佐剂在结核融合蛋白疫苗加强卡介苗(BCG)免疫中的不同免疫辅助效应.方法 选择DDA、BCG-PSN作为融合蛋白AMM(Ag85B-MPT64190-198-Mtb8.4)的佐剂,在BCG初免小鼠后,AMM疫苗加强免疫两次,其中一组联合使用两种佐剂(DDA/BCG-PSN),另一组单独以DDA作为佐剂,同时设立BCG或磷酸缓冲液(PBS)免疫组为对照.应用ELISA及ELISPOT检测免疫小鼠的体液与细胞免疫反应,最后一次加强免疫后第12周,以H37Rv尾静脉攻毒并检测小鼠肺脾组织细菌载量和病理改变,评价不同佐剂疫苗的保护效果.结果 在BCG初免基础上,联合佐剂组(AMM/DDA/BCG-PSN)和单独佐剂组(AMM/DDA)加强免疫两次后,脾脏淋巴细胞经抗原Ag85B和PPD(purified protein derivative)刺激后,皆可产生分泌较BCG组高的IFN-γ.毒力株攻击后菌落形成单位(colony-forming unit,CFU)计数显示,联合佐剂组(AMM/DDA/BCG-PSN)脾脏荷菌量少于PBS组和BCG组(P<0.05);而单独佐剂组(AMM/DDA)肺部荷菌量少于PBS组和BCG组(P<0.05).组织病理分析结果 表明AMM/DDA/BCG-PSN组肺组织病理损伤较轻,而AMM/DDA组病理损伤个体差异较大.结论 DDA是较为理想的结核亚单位疫苗佐剂,能诱导较强的细胞免疫和免疫保护作用;BCG-PSN可能具有免疫调节作用,可以减轻免疫病理损伤.     

The Mycobacterium tuberculosis recombinant 27-kilodalton lipoprotein induces a strong Th1-type immune response deleterious to protection

Th1 immune response is essential in the protection against mycobacterial intracellular pathogens. Lipoproteins trigger both humoral and cellular immune responses and may be candidate protective antigens. We studied in BALB/c mice the immunogenicity and the protection offered by the recombinant 27-kDa Mycobacterium tuberculosis lipoprotein and the corresponding DNA vaccine. Immunization with the 27-kDa antigen resulted in high titers of immunoglobulin G1 (IgG1) and IgG2a with a typical Th1 profile and a strong delayed hypersensitivity response. A strong proliferation response was observed in splenocytes, and significant nitric oxide production and gamma interferon secretion but not interleukin 10 secretion were measured. Based on these criteria, the 27-kDa antigen induced a typical Th1-type immune response thought to be necessary for protection. Surprisingly, in 27-kDa-vaccinated mice (protein or DNA vaccines) challenged by M. tuberculosis H37Rv or BCG strains, there was a significant increase in the numbers of CFU in the spleen compared to that for control groups. Furthermore, the protection provided by BCG or other mycobacterial antigens was completely abolished once the 27-kDa antigen was added to the vaccine preparations. This study indicates that the 27-kDa antigen has an adverse effect on the protection afforded by recognized vaccines. We are currently studying how the 27-kDa antigen modulates the mouse immune response.